The present invention relates generally to means for reducing and/or stopping the vibration occurring on spans of overhead conductors, and more particularly to a relatively small, lightweight and inexpensive seismic damping device for attachment to an overhead conductor to dampen vibration thereof.
Heretofore, the device that has been used extensively in damping the vibration of single overhead conductors has been the Stockbridge damper. As is well known, such a device employs a stranded steel cable supporting weights on opposed ends of the cable, the cable being connected to a conductor by way of clamping means. The Stockbridge damper uses friction among the strands of the cable to dissipate the energy of the wind received by the conductor in the form of heat. Three U.S. patents describing such dampers are U.S. Pat. Nos. 1,992,538 to Monroe et al, 2,058,173 to Noyes et al and 2,094,899 to MacIntyre.
A damping device employing two elastomer washers mounted between opposed inertial weights and a clamp arm is shown in U.S. Pat. No. 2,271,935 to Buchanan et al. The device is mounted on the conductor such that it extends horizontally from the conductor. The vertical motion of the conductor is converted to a twisting motion by the weights. Other motions of the weights appear to be precluded, as the elastomer washers are compressed into a space provided between the clamp arm and a bolt securing the weights to the arm.
U.S. Pat. No. 3,478,160 to Reed shows a damping device in which a weight is connected to a clamp arm via a single rubber bushing. The center of gravity of the weight is offset from the location of weight suspension, and the weight is nonsymmetrical about three mutually orthogonal plans, all passing through the center of gravity.
The washers and bushings of Buchanan et al and Reed function to dissipate the energy of conductor vibration by virtue of hysteresis losses in the elastomer material, as opposed to the sliding friction that takes place between adjacent metal strands in the Stockbridge damper.